How to fix 100% cpu usage?

[Storm]

Another angle is overheating. If the CPU is too hot it can get stuck in a cycle where everything feels slow and maxed out.

Dust buildup is a huge factor on older machines. Fans clog up, airflow drops, and performance tanks.

Cleaning it out can sometimes do more than any software tweak.

[Courier53]

Also worth checking if you are still on a mechanical hard drive. Old drives plus modern Windows can cause constant background strain that looks like CPU usage.

The system ends up waiting on disk operations and everything feels pegged.

An SSD upgrade often fixes the feeling of a constantly stressed system.

[Andy99]

Low RAM can also indirectly cause 100 percent CPU usage. When memory runs out, the system starts swapping constantly.

That creates extra load and everything spirals into slowness.

Even adding a small amount of RAM can change the behavior a lot.

[Hannah56]

If you are running a lot of browser tabs, that alone can push older CPUs to their limit. Modern websites are surprisingly heavy.

Each tab is basically a mini application now, not just a page.

Closing a few can instantly bring usage down.

[Compiled Wolf]

Do not ignore the possibility of malware or crypto mining software. Old PCs are easy targets if nothing has been cleaned in a while.

If CPU usage is high even when idle, that is a red flag.

A full scan with a decent tool is worth doing.